[RFC 11/18] limits: track and present RLIMIT_NPROC actual max

[Topi Miettinen]

Track maximum number of processes per user and present it
in /proc/self/limits.

Signed-off-by: Topi Miettinen <toiwoton@xxxxxxxxx>
---
 fs/proc/base.c        | 4 ++++
 include/linux/sched.h | 1 +
 kernel/fork.c         | 5 +++++
 kernel/sys.c          | 5 +++++
 4 files changed, 15 insertions(+)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 1df4fc8..02576c6 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -670,6 +670,10 @@ static int proc_pid_limits(struct seq_file *m, struct pid_namespace *ns,
 				seq_printf(m, "%-20lu\n", psecs);
 			}
 			break;
+		case RLIMIT_NPROC:
+			seq_printf(m, "%-20d\n",
+				   atomic_read(&task->real_cred->user->max_processes));
+			break;
 		default:
 			seq_printf(m, "%-20lu\n",
 				   task->signal->rlim_curmax[i]);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 0150380..feb9bb7 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -838,6 +838,7 @@ static inline int signal_group_exit(const struct signal_struct *sig)
 struct user_struct {
 	atomic_t __count;	/* reference count */
 	atomic_t processes;	/* How many processes does this user have? */
+	atomic_t max_processes;	/* How many processes has this user had at the same time? */
 	atomic_t sigpending;	/* How many pending signals does this user have? */
 #ifdef CONFIG_INOTIFY_USER
 	atomic_t inotify_watches; /* How many inotify watches does this user have? */
diff --git a/kernel/fork.c b/kernel/fork.c
index 5c2c355..667290f 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1653,6 +1653,11 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	trace_task_newtask(p, clone_flags);
 	uprobe_copy_process(p, clone_flags);
 
+	if (atomic_read(&p->real_cred->user->max_processes) <
+	    atomic_read(&p->real_cred->user->processes))
+		atomic_set(&p->real_cred->user->max_processes,
+			   atomic_read(&p->real_cred->user->processes));
+
 	return p;
 
 bad_fork_cancel_cgroup:
diff --git a/kernel/sys.c b/kernel/sys.c
index 6629f6f..955cf21 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -439,6 +439,11 @@ static int set_user(struct cred *new)
 	else
 		current->flags &= ~PF_NPROC_EXCEEDED;
 
+	if (atomic_read(&new_user->max_processes) <
+	    atomic_read(&new_user->processes))
+		atomic_set(&new_user->max_processes,
+			   atomic_read(&new_user->processes));
+
 	free_uid(new->user);
 	new->user = new_user;
 	return 0;
-- 
2.8.1